Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper for easier cleanup.
In a small bowl, whisk together the olive oil, minced garlic, oregano, salt, and pepper.
Place the trimmed asparagus on one side of the prepared baking sheet. Drizzle half of the oil mixture over the asparagus and toss to coat evenly. Spread the asparagus into a single layer.
Place the salmon fillets on the other side of the baking sheet. Brush the remaining oil mixture evenly over the tops of the salmon fillets.
Arrange a few thin lemon slices on top of each salmon fillet.
Bake for 12 to 15 minutes, or until the salmon is cooked through and flakes easily with a fork, and the asparagus is tender-crisp. Cooking time depends on the thickness of your salmon.
Remove from the oven. Garnish the dish with fresh chopped parsley before serving.
Notes
For thicker salmon fillets, you may need to add 2 to 3 minutes to the cooking time.
You can substitute broccoli florets or green beans for the asparagus. Adjust cooking time if using denser vegetables.
Use fresh lemon juice over the finished dish for extra brightness if desired.